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docs(world-id): fix on-chain action hash to use field-reduced value #191

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Merged
soamdesai-tfh merged 5 commits into from
Sep 23, 2026
Merged

docs(world-id): fix on-chain action hash to use field-reduced value #191

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5d3d5b0
docs(world-id): fix on-chain action hash to use field-reduced value
soamdesai-tfh Sep 21, 2026
738be27
polish: tighten wording on hash_to_field mapping, match house style
soamdesai-tfh Sep 21, 2026
9471513
Merge branch 'main' into docs-audit/world-id-onchain-hash-fix
soamdesai-tfh Sep 21, 2026
4820e77
docs(world-id): clarify unreduced action hash failures
soamdesai-tfh Sep 23, 2026
79654aa
docs(world-id): name the bytes hashed for the on-chain action
soamdesai-tfh Sep 23, 2026
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6 changes: 5 additions & 1 deletion world-id/idkit/onchain-verification.mdx
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Expand Up @@ -167,11 +167,15 @@ contract VerifyUniquenessV4 {

Minimal mapping from IDKit result:
- `nullifier` = `responses[i].nullifier`
- `action` = `keccak256(action)` as `uint256`
- `action` = `hash_to_field(utf8(action))` as `uint256`, over the UTF-8 bytes of the top-level `action` string (same field-reduction as [RP signatures](/world-id/idkit/signatures#algorithm))
- `rpId` = numeric form of your `rp_context.rp_id` (the `rp_`-prefixed string from your RP context, not the result)
- `nonce` = top-level `nonce`
- `signalHash` = `responses[i].signal_hash`
- `expiresAtMin` = `responses[i].expires_at_min`
- `issuerSchemaId` = `responses[i].issuer_schema_id`
- `credentialGenesisIssuedAtMin` = the request's `genesis_issued_at_min` constraint (`0` if unconstrained) — not returned in `responses[i]`
- `proof` = `responses[i].proof` (`uint256[5]`)

<Warning>
Use `hash_to_field(utf8(action))`, which in Solidity is `uint256(keccak256(bytes(action))) >> 8`. An unreduced hash can exceed the BN254 scalar field and revert with `PublicInputNotInField`; even when it fits, it does not match the field-reduced action used by the proof.
</Warning>
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